Congestion window control based on queuing delay and packet loss

ABSTRACT

A method of controlling size of a congestion window, includes, at a transmitting device, transmitting a plurality of data packets over a communication channel from the transmitting device to a receiver, determining a queuing delay and a loss rate of the transmission, comparing the queuing delay to a threshold queuing delay, comparing the loss rate to a threshold loss rate, and in response to a determination that the queuing delay is greater than the threshold queuing delay and the loss rate is greater than the threshold loss rate, resetting the size of the congestion window in accordance with a function of the current size of the congestion window, the queuing delay, and the loss rate, wherein at equilibrium the function generates a value inversely proportional to a weighted sum of an excess queuing delay and an excess loss rate.

RELATED APPLICATION

This application claims priority on U.S. Provisional Application Ser.No. 61/326,985, filed Apr. 22, 2010, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The disclosed embodiments relate generally to transmitting data viacommunication networks. More particularly, the disclosed embodimentsrelate to controlling size of a congestion window utilized by atransmitting device.

BACKGROUND

Computer networks allow communication between one or more recipients.When the number of transmitters and receivers, and the amount of packettraffic, is greater than the network can efficiently handle (i.e., thenetwork is congested), delay of transmission of packets to receiversand/or packet loss occurs. Congestion problems can be handled byadjusting the size of a congestion window, which corresponds to theamount of data that can be sent to a recipient before an acknowledgmentis received, in accordance with network conditions.

SUMMARY

In order to maximize the amount of data transmitted to a receiverwithout overwhelming the network, the amount of data sent by atransmitting device to a receiver can be controlled by resetting (i.e.,adjusting) the size of a congestion window in response to networkconditions, including queuing delay and/or packet loss.

A method of controlling the size of a congestion window includes, at atransmitting device, transmitting a number of data packets over acommunication channel from the transmitting device to a receiver,determining a queuing delay of the transmission, wherein the queuingdelay corresponds to the difference of an average round trip time of thedata packets and a base round trip time of the data packets, anddetermining a loss rate of the transmission, wherein the loss ratecorresponds to the ratio of the number of data packets lost in thetransmission to the number of data packets transmitted. The methodfurther includes comparing the queuing delay to a threshold queuingdelay and comparing the loss rate to a threshold loss rate. In responseto a determination that the queuing delay is greater than the thresholdqueuing delay and the loss rate is less than the threshold loss rate,resetting the size of the congestion window in accordance with a firstfunction of a current size of the congestion window and the queuingdelay, wherein at equilibrium the first function generates a valueinversely related to an excess queuing delay, which corresponds to thedifference between the queuing delay and the threshold queuing delay.Further, in response to a determination that the queuing delay is lessthan the threshold queuing delay and the loss rate is greater than thethreshold loss rate, resetting the size of the congestion window inaccordance with a second function of the current size of the congestionwindow and the loss rate, wherein at equilibrium the second functiongenerates a value inversely related to an excess loss rate, whichcorresponds to the difference between the loss rate and the thresholdloss rate. And in response to a determination that the queuing delay isgreater than the threshold queuing delay and the loss rate is greaterthan the threshold loss rate, resetting the size of the congestionwindow in accordance with a third function of the current size of thecongestion window, the queuing delay, and the loss rate, wherein atequilibrium the third function generates a value inversely proportionalto a weighted sum of the excess queuing delay and excess loss rate. Insome embodiments, the weighted sum is a convex sum. A convex sum is alinear combination of values where all coefficients are non-negative andsum up to 1.

An apparatus for controlling the size of a congestion window includes atransceiver to transmit a plurality of packets over a communicationchannel to a receiver, one or more processors, and memory for storinginstructions to be executed by the one or more processors. The storedinstructions include instructions to determine a queuing delay of thetransmission, wherein the queuing delay corresponds to the difference ofan average round trip time of the data packets and a base round triptime of the data packets, determine a loss rate of the transmission,wherein the loss rate corresponds to the ratio of a number of datapackets lost in the transmission to the number of data packetstransmitted. The stored instructions further include: instructions tocompare the queuing delay to a threshold queuing delay, and compare theloss rate to a threshold loss rate; and instructions to, in response toa determination that the queuing delay is greater than the thresholdqueuing delay and the loss rate is less than the threshold loss rate,reset the size of the congestion window in accordance with a firstfunction of a current size of the congestion window and the queuingdelay, wherein at equilibrium the first function generates a valueinversely related to an excess queuing delay, which corresponds to thedifference between the queuing delay and the threshold queuing delay.Further, the stored instructions include instructions to, in response toa determination that the queuing delay is less than the thresholdqueuing delay and the loss rate is greater than the threshold loss rate,reset the size of the congestion window in accordance with a secondfunction of the current size of the congestion window and the loss rate,wherein at equilibrium the second function generates a value inverselyrelated to an excess loss rate, which corresponds to the differencebetween the loss rate and the threshold loss rate. Additionally, thestored instructions include instructions to, in response to adetermination that the queuing delay is greater than the thresholdqueuing delay and the loss rate is greater than the threshold loss rate,reset the size of the congestion window in accordance with a thirdfunction of the current size of the congestion window, the queuingdelay, and the loss rate, wherein at equilibrium the third functiongenerates a value inversely proportional to a weighted sum of the excessqueuing delay and excess loss rate. In some embodiments, the weightedsum is a convex sum.

A computer readable storage medium, storing one or more programs forexecution by one or more processor of an apparatus that includes atransceiver to transmit packets over a communication channel to areceiver is also disclosed. The one or more programs are for executionby the one or more processors of the apparatus so as to perform a methodthat includes transmitting a number of data packets over a communicationchannel from the transmitting device to a receiver, determining aqueuing delay of the transmission, wherein the queuing delay correspondsto the difference of an average round trip time of the data packets anda base round trip time of the data packets, and determining a loss rateof the transmission, wherein the loss rate corresponds to the ratio ofthe number of data packets lost in the transmission to the number ofdata packets transmitted. The method also includes comparing the queuingdelay to a threshold queuing delay and comparing the loss rate to athreshold loss rate. The method further includes, in response to adetermination that the queuing delay is greater than the thresholdqueuing delay and the loss rate is less than the threshold loss rate,resetting the size of the congestion window in accordance with a firstfunction of a current size of the congestion window and the queuingdelay, wherein at equilibrium the first function generates a valueinversely related to an excess queuing delay, which corresponds to thedifference between the queuing delay and the threshold queuing delay.The method also includes, in response to a determination that thequeuing delay is less than the threshold queuing delay and the loss rateis greater than the threshold loss rate, resetting the size of thecongestion window in accordance with a second function of the currentsize of the congestion window and the loss rate, wherein at equilibriumthe second function generates a value inversely related to an excessloss rate, which corresponds to the difference between the loss rate andthe threshold loss rate. Additionally, the method includes, in responseto a determination that the queuing delay is greater than the thresholdqueuing delay and the loss rate is greater than the threshold loss rate,resetting the size of the congestion window in accordance with a thirdfunction of the current size of the congestion window, the queuingdelay, and the loss rate, wherein at equilibrium the third functiongenerates a value inversely proportional to a weighted sum of the excessqueuing delay and excess loss rate. In some embodiments, the weightedsum is a convex sum.

A method of controlling size of a congestion window includes, at atransmitting device, transmitting a plurality of data packets over acommunication channel from the transmitting device to a receiver,determining a queuing delay of the transmission, wherein the queuingdelay is the difference of an average round trip time of the datapackets and a base round trip time of the data packets, determining aloss rate of the transmission, wherein the loss rate is the ratio of anumber of data packets lost in the transmission to the number of datapackets transmitted, determining an excess queuing delay, wherein excessqueuing delay is the difference between the queuing delay and thethreshold queuing delay, determining an excess loss rate, wherein excessloss rate is the difference between the loss rate and the threshold lossrate, comparing the queuing delay to a threshold queuing delay,comparing the loss rate to a threshold loss rate, and, in response to adetermination that the queuing delay is greater than the thresholdqueuing delay and the loss rate is greater than the threshold loss rate,resetting the size of the congestion window in accordance with afunction of the current size of the congestion window, the queuingdelay, and the loss rate, wherein at equilibrium the function generatesa value inversely proportional to a weighted sum of the excess queuingdelay and excess loss rate. In some embodiments, the weighted sum is aconvex sum.

An apparatus for controlling size of a congestion window includes atransceiver to transmit a plurality of packets over a communicationchannel to a receiver, one or more processors, and memory for storinginstructions to be executed by the one or more processors. The storedinstructions include instructions to transmit a plurality of datapackets over a communication channel from the transmitting device to areceiver, determine a queuing delay of the transmission, wherein thequeuing delay is the difference of an average round trip time of thedata packets and a base round trip time of the data packets, determine aloss rate of the transmission, wherein the loss rate is the ratio of anumber of data packets lost in the transmission to the number of datapackets transmitted, determine an excess queuing delay, wherein excessqueuing delay is the difference between the queuing delay and thethreshold queuing delay, determine an excess loss rate, wherein excessloss rate is the difference between the loss rate and the threshold lossrate, compare the queuing delay to a threshold queuing delay, comparethe loss rate to a threshold loss rate, and, in response to adetermination that the queuing delay is greater than the thresholdqueuing delay and the loss rate is greater than the threshold loss rate,reset the size of the congestion window in accordance with a function ofthe current size of the congestion window, the queuing delay, and theloss rate, wherein at equilibrium the function generates a valueinversely proportional to a weighted sum of the excess queuing delay andexcess loss rate. In some embodiments, the weighted sum is a convex sum.

A computer readable storage medium, storing one or more programs forexecution by one or more processor of an apparatus that includes atransceiver to transmit packets over a communication channel to areceiver is also disclosed. The one or more programs are for executionby the one or more processors of the apparatus so as to perform a methodincluding transmitting a plurality of data packets over a communicationchannel from the transmitting device to a receiver, determining aqueuing delay of the transmission, wherein the queuing delay is thedifference of an average round trip time of the data packets and a baseround trip time of the data packets, determining a loss rate of thetransmission, wherein the loss rate is the ratio of a number of datapackets lost in the transmission to the number of data packetstransmitted, determining an excess queuing delay, wherein excess queuingdelay is the difference between the queuing delay and the thresholdqueuing delay, determining an excess loss rate, wherein excess loss rateis the difference between the loss rate and the threshold loss rate,comparing the queuing delay to a threshold queuing delay, comparing theloss rate to a threshold loss rate, and, in response to a determinationthat the queuing delay is greater than the threshold queuing delay andthe loss rate is greater than the threshold loss rate, resetting thesize of the congestion window in accordance with a function of thecurrent size of the congestion window, the queuing delay, and the lossrate, wherein at equilibrium the function generates a value inverselyproportional to a weighted sum of the excess queuing delay and excessloss rate. In some embodiments, the weighted sum is a convex sum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a system for controlling the sizeof a congestion window in accordance with some embodiments of thepresent invention.

FIG. 2 is a flow diagram illustrating a process for controlling the sizeof a congestion window at a transmitting device in accordance with someembodiments of the present invention.

FIG. 3 is a flow diagram illustrating a process for controlling the sizeof a congestion window at a transmitting device in accordance with someembodiments of the present invention.

Like reference numerals refer to corresponding parts throughout thedrawings.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a block diagram illustrating a system 100 for controlling thesize of a congestion window. A transmitting device 110 transmits packetsto a receiver 150 via a communication network 140 in accordance with acongestion window cwnd (not shown). The transmitting device 110 alsoreceives acknowledgment packets (ACKs) from the receiver 150 via thecommunication network 140. Transmitting device 110 may also be referredto herein as a transceiver, as it both transmits and receivesinformation.

The congestion window cwnd corresponds to the amount of outstanding data(unacknowledged by the receiver 150) the transmitting device 110 cansend on a particular connection before it gets acknowledgment packets(ACKs) back from the receiver 150. As described below, the size of thecongestion window cwnd is dynamically adjusted in response tocommunication network 140 conditions.

The communication network 140 may be any local area network (LAN) and/orwide area network (WAN), such as an intranet, an extranet, the Internet,or a combination of such networks. It is sufficient that thecommunication network 140 provides communication capability between thetransmitting device 110 and the receiver 150. In some embodiments, thecommunication network 140 transports packets using FAST TransmissionControl Protocol (FAST TCP).

The transmitter 110 and the receiver 150 are both connected to thecommunication network 140 during transmission of packets betweentransmitter 110 and receiver 150. Receiver 150 receives and processesthe packets transmitted by transmitting device 110. Receiver 150 alsogenerates acknowledgment packets (ACKs) corresponding to each of thetransmitted packets.

Transmitting device 110 typically includes one or more network or othercommunication interfaces 112, one or more processors 114, and memory116.

Memory 116 includes high-speed random access memory, such as DRAM, SRAM,DDR RAM or other random access solid state memory devices; and mayinclude non-volatile memory, such as one or more magnetic disk storagedevices, optical disk storage devices, flash memory devices, or othernon-volatile solid state storage devices. Memory 116 may optionallyinclude one or more storage devices remotely located from processor 114.Memory 116, or alternately the non-volatile memory device(s) withinmemory 116, comprises a computer readable storage medium. In someembodiments, memory 116 stores the following programs, modules and datastructures, or a subset thereof:

-   -   an operating system 118 that includes procedures for handling        various basic system services and for performing hardware        dependent tasks;    -   a communications module 120 that is used for connecting the        transmitting device 110 to a receiver 150 via the one or more        communication interfaces 112 (wired or wireless) and one or more        communication networks 140, such as the Internet, other wide        area networks, local area networks, metropolitan area networks,        and so on;    -   a congestion window control module 122 that includes a parameter        determination module 124;    -   a compare module 132; and    -   content 134, which includes data to be transmitted.

The parameter determination module 124 may include a round trip time(RTT) determination module 126, a queuing delay determination module128, and a loss rate determination module 130.

The round trip time (RTT) determination module 126 determines a currentround trip time value, RTT(t), for use by the congestion window controlmodule 122 to control a size of the congestion window cwnd(t).Generally, RTT(t) is the time required for a transmitted packet totravel from the transmitting device 110 to the receiver 150 and for acorresponding ACK to travel back from the receiver 150 to thetransmitting device 110.

The queuing delay determination module 128 determines a queuing delayq(t) for use by the congestion window control module 122 to control thesize of the congestion window cwnd(t). Generally, queuing delay q(t) isthe difference of an average RTT of the packets and a base RTT. The baseRTT is the shortest RTT seen by the transmitting device 110 since thetransmitting device 110 has transmitted packets on a particularconnection.

The loss rate determination module 130 determines a current loss ratel(t) for use by the congestion window control module 122 to control thesize of the congestion window cwnd(t). Generally, the current loss ratel(t) is the ratio of the number of data packets lost in the transmissionto the number of data packets transmitted.

The congestion window control module 122 controls the size of thecongestion window cwnd(t). In some embodiments, the congestion windowcontrol module 122 resets the size of the congestion window cwnd(t+1) inaccordance with:

$\begin{matrix}{{{cwnd}\left( {t + 1} \right)} = {{\left( {1 - {\lambda\frac{\left\lbrack {{q(t)} - q_{0}} \right\rbrack^{+}}{{q(t)} + d}} - {\overset{\_}{\lambda}\left\lbrack {{l(t)} - l_{0}} \right\rbrack}^{+}} \right){{cwnd}(t)}} + \alpha}} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$wherein λε(0,1) is a constant parameter, q₀ is a queuing delaythreshold, d is an estimate of a round trip propagation delay and fixedprocessing time (usually set to the base RTT), l₀ is a packet lossthreshold, and α is a parameter representing an equilibrium point forupdates to the congestion window. The function [x]⁺=max(x,0). In someembodiments, λ=1−λ, and thus λε(0,1).

The congestion window control module 122 works to stabilize the size ofthe congestion window cwnd(t) such that the reset size of the congestionwindow cwnd(t+1) is equal to the current size of the congestion windowcwnd(t) at equilibrium. In some embodiments, the size of the congestionwindow cwnd(t) is reset (i.e., recomputed, based on the most recentlydetermined RTT(t), q(t), and l(t) values) once every round trip time. Inother embodiments, the size of the congestion window cwnd(t) is resetperiodically (e.g., every N milliseconds).

At equilibrium, when the size of the congestion window cwnd(t) isstabilized (i.e., cwnd(t+1)=cwnd(t)=cwnd), the congestion window controlmodule 122 sets the size of the congestion window cwnd(t) in accordancewith:

$\begin{matrix}{{cwnd} = \frac{\alpha}{{{\lambda\left\lbrack {q - q_{0}} \right\rbrack}^{+}/T} + {\overset{\_}{\lambda}\left\lbrack {l - l_{0}} \right\rbrack}^{+}}} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$where cwnd, q, and l are the equilibrium values of cwnd(t), q(t), andl(t), respectively, and T=q+d, which is the equilibrium round trip time,RTT.

At equilibrium, updates to the size of the congestion window settle intothree regions: the delay region, where queuing delay dominates (i.e.,q>q₀ and l≦l₀); the loss region, where packet loss rate dominates (i.e.,q≦q₀ and l>l₀); and the weighted sum region, where both queuing delayand packet loss are significant (i.e., q>q₀ and l>l₀). The equilibriumcongestion window cwnd size in each of these three regions is describedby:

$\begin{matrix}{{{Delay}\mspace{14mu}{region}\text{:}\mspace{14mu}{cwnd}} = {{\frac{\alpha}{{\lambda\left( {q - q_{0}} \right)}/T}\mspace{14mu}{when}\mspace{14mu} q} > {q_{0}\mspace{14mu}{and}\mspace{14mu} l} \leq l_{0}}} & \left( {{Eq}.\mspace{14mu} 3} \right) \\{{{Loss}\mspace{14mu}{region}\text{:}\mspace{14mu}{cwnd}} = {{\frac{\alpha}{\overset{\_}{\lambda}\left( {l - l_{0}} \right)}\mspace{14mu}{when}\mspace{14mu} q} \leq {q_{0}\mspace{14mu}{and}\mspace{14mu} l} > l_{0}}} & \left( {{Eq}.\mspace{14mu} 4} \right) \\{{{Weighted}\mspace{14mu}{sum}\mspace{14mu}{region}\text{:}\mspace{14mu}{cwnd}} = {{\frac{\alpha}{{{\lambda\left( {q - q_{0}} \right)}/T} + {\overset{\_}{\lambda}\left( {l - l_{0}} \right)}}\mspace{14mu}{when}\mspace{14mu} q} > {q_{0}\mspace{14mu}{and}\mspace{14mu} l} > l_{0}}} & \left( {{Eq}.\mspace{14mu} 5} \right)\end{matrix}$

Returning to FIG. 1, the compare module 132 compares the queuing delay qand a threshold queuing delay q₀. In some embodiments, the thresholdqueuing delay q₀ is set to a default parameter. In other embodiments,the threshold queuing delay q₀ is dependent upon network conditions(e.g., in some embodiments, q₀ is set to the minimum value of qobserved, on the same communication channel, since the last time a resetor power on event occurred). The compare module 132 also compares lossrate l and a threshold loss rate l₀. In some embodiments, the thresholdloss rate l₀ is set to a default parameter. In other embodiments, thethreshold loss rate l₀ is dependent upon network conditions (e.g., insome embodiments, l₀ is set to the minimum value of l observed, on thesame communication channel, since the last time a reset or power onevent occurred).

As shown above, when the queuing delay q is greater than the thresholdqueuing delay q₀ and the loss rate l is less than or equal to thethreshold loss rate l₀, the congestion control module 122 operates inthe delay region and the size of the congestion window cwnd is reset inaccordance with Eq. 3. As shown in Eq. 3, the cwnd reset functiongenerates a cwnd equilibrium value inversely proportional to an excessqueuing delay, which corresponds to a difference between the queuingdelay q and the threshold queuing delay q₀, when the congestion controlmodule 122 is operating in the delay region.

Further, when the queuing delay q is less than or equal to the thresholdqueuing delay q₀ and the loss rate l is greater than the threshold lossrate l₀, the congestion control module 122 operates in the loss regionand the size of the congestion window cwnd is reset in accordance withEq. 4. As shown in Eq. 4, the cwnd reset function generates a cwnd valueinversely proportional to an excess loss rate, which corresponds to adifference between the loss rate l and the threshold loss rate l₀, whenthe congestion control module 122 is operating in the loss region.

Additionally, when the queuing delay q is greater than the thresholdqueuing delay q₀ and the loss rate l is greater than the threshold lossrate l₀, the congestion control module 122 operates in the weighted sumregion and the size of the congestion window cwnd is reset in accordancewith Eq. 5. As shown in Eq. 5, the cwnd reset function generates a cwndvalue inversely proportional to a weighted sum of the excess queuingdelay and the excess loss rate when the congestion control module 122 isoperating in the weighted sum region. In some embodiments, the weightedsum (in the cwnd reset function, e.g., the cwnd reset function shown inEq. 5) is a convex sum.

As stated above, the transmitting device 110 transmits packets to thereceiver 150 in accordance with congestion window cwnd(t). Accordingly,after the congestion window cwnd(t) is reset, the transmitting device110 transmits packets over communication channel 140 to the receiver 150in accordance with the reset size of the congestion window cwnd(t).

Each of the above identified elements may be stored in one or more ofthe previously mentioned memory devices of transmitter 110. Theapplications, functions, modules, and operating system shown in FIG. 1correspond to a set of instructions, stored in memory, for performingthe functions described above. The set of instructions can be executedby the one or more processors 114 of transmitter 110. The aboveidentified modules or programs (i.e., sets of instructions) need not beimplemented as separate software programs, procedures or modules, andthus various subsets of these modules may be combined or otherwisere-arranged in various embodiments. In some embodiments, memory 116 or acomputer readable storage medium of memory 116 stores a subset of themodules and data structures identified above. Furthermore, memory 116 ora computer readable storage medium of memory 116 may store additionalmodules and data structures not described above.

Although FIG. 1 shows a transmitting device 110, it is intended more asfunctional description of the various features which may be present in atransmitting device or transceiver. In practice, and as recognized bythose of ordinary skill in the art, items shown separately could becombined and some items could be separated.

FIG. 2 is a flow chart of a method 200 for controlling size of acongestion window. The following operations are performed at atransmitting device (e.g., transmitting device 110 (FIG. 1)).

A number of data packets are transmitted over a communication channel(e.g., communication network 140 (FIG. 1)) from the transmitting deviceto a receiver (e.g., receiver 150 (FIG. 1)) (202).

A queuing delay (e.g., queuing delay q) of the transmission thetransmission is determined (204). As discussed above in connection withFIG. 1, the queuing delay corresponds to the difference of an averageround trip time of the data packets and a base round trip time of thedata packets. As further described above in connection with FIG. 1, theround trip time is the time required for a transmitted packet to travelfrom the transmitting device to the receiver and ACKs to travel back.

A loss rate (e.g., loss rate l) of the transmission is also determined(206). As discussed above in connection with FIG. 1, the loss ratecorresponds to the ratio of the number of data packets lost in thetransmission to the number of data packets transmitted.

The method 200 further includes comparing the queuing delay to athreshold queuing delay (e.g., threshold queuing delay q₀) (208) andcomparing the loss rate to a threshold loss rate (e.g., threshold lossrate l₀) (210).

In response to a determination that the queuing delay is greater thanthe threshold queuing delay and the loss rate is less than the thresholdloss rate, the method 200 includes resetting the size of the congestionwindow in accordance with a first function of a current size of thecongestion window and the queuing delay (212). At equilibrium, the firstfunction (e.g., Eq. 3) generates a value inversely related to an excessqueuing delay, which, as explained above in connection with FIG. 1,corresponds to the difference between the queuing delay and thethreshold queuing delay.

In response to a determination that the queuing delay is less than thethreshold queuing delay and the loss rate is greater than the thresholdloss rate, the method 200 includes resetting the size of the congestionwindow in accordance with a second function of the current size of thecongestion window and the loss rate (214). At equilibrium, the secondfunction (e.g., Eq. 4) generates a value inversely related to an excessloss rate, which, as explained above in connection with FIG. 1,corresponds to the difference between the loss rate and the thresholdloss rate.

In response to a determination that the queuing delay is greater thanthe threshold queuing delay and the loss rate is greater than thethreshold loss rate, the method 200 includes resetting the size of thecongestion window in accordance with a third function of the currentsize of the congestion window, the queuing delay, and the loss rate(216). At equilibrium, the third function (e.g., Eq. 5) generates avalue inversely proportional to a weighted sum of the excess queuingdelay and excess loss rate. In some embodiments, the weighted sum is aconvex sum (218).

FIG. 3 is a flow chart of a method 300 for controlling size of acongestion window. The following operations are performed at atransmitting device (e.g., transmitting device 110 (FIG. 1)).

A plurality of data packets are transmitted over a communication channel(e.g., communication network 140 (FIG. 1)) from the transmitting deviceto a receiver (e.g., receiver 150 (FIG. 1)) (302).

A queuing delay (e.g., queuing delay q) of the transmission isdetermined (304). As discussed above in connection with FIG. 1, thequeuing delay corresponds to the difference of an average round triptime of the data packets and a base round trip time of the data packets.As further described above in connection with FIG. 1, the round triptime is the time required for a transmitted packet to travel from thetransmitting device to the receiver and the correspondingacknowledgement (ACK) to travel back.

A loss rate (e.g., loss rate l) of the transmission is determined (306).As discussed above in connection with FIG. 1, the loss rate correspondsto the ratio of the number of data packets lost in the transmission tothe number of data packets transmitted.

The method 300 further includes comparing the queuing delay to athreshold queuing delay (e.g., threshold queuing delay q₀) (308) andcomparing the loss rate to a threshold loss rate (e.g., threshold lossrate l₀) (310).

An excess queuing delay is determined (312). As discussed above inconnection with FIG. 1, excess queuing delay is the difference betweenthe queuing delay and the threshold queuing delay.

An excess loss rate is determined (314). As discussed above inconnection with FIG. 1, excess loss rate is the difference between theloss rate and the threshold loss rate.

In response to a determination that the queuing delay is greater thanthe threshold queuing delay and the loss rate is greater than thethreshold loss rate, method 300 includes resetting the size of thecongestion window in accordance with a function of the current size ofthe congestion window, the queuing delay, and the loss rate (316). Atequilibrium, the function (e.g., Eq. 5) generates a value (congestionwindow size) inversely proportional to a weighted sum of the excessqueuing delay and excess loss rate. In some embodiments, the weightedsum is a convex sum (318).

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A method of controlling size of a congestionwindow, comprising: at a transmitting device: transmitting a number ofdata packets over a communication channel from the transmitting deviceto a receiver; determining a queuing delay of the transmission, whereinthe queuing delay corresponds to the difference of an average round triptime of the data packets and a base round trip time of the data packets;determining a loss rate of the transmission, wherein the loss ratecorresponds to the ratio of a number of data packets lost in thetransmission to the number of data packets transmitted; comparing thequeuing delay to a threshold queuing delay; comparing the loss rate to athreshold loss rate; in response to a determination that the queuingdelay is greater than the threshold queuing delay and the loss rate isless than the threshold loss rate, resetting the size of the congestionwindow in accordance with a first function of a current size of thecongestion window and the queuing delay, wherein at equilibrium thefirst function generates a value inversely related to an excess queuingdelay, which corresponds to the difference between the queuing delay andthe threshold queuing delay; in response to a determination that thequeuing delay is less than the threshold queuing delay and the loss rateis greater than the threshold loss rate, resetting the size of thecongestion window in accordance with a second function of the currentsize of the congestion window and the loss rate, wherein at equilibriumthe second function generates a value inversely related to an excessloss rate, which corresponds to the difference between the loss rate andthe threshold loss rate; in response to a determination that the queuingdelay is greater than the threshold queuing delay and the loss rate isgreater than the threshold loss rate, resetting the size of thecongestion window in accordance with a third function of the currentsize of the congestion window, the queuing delay, and the loss rate,wherein at equilibrium the third function generates a value inverselyproportional to a weighted sum of the excess queuing delay and excessloss rate.
 2. The method of claim 1, wherein the weighted sum is aconvex sum.
 3. An apparatus for controlling size of a congestion window,the apparatus comprising: a transceiver to transmit a plurality ofpackets over a communication channel to a receiver; one or moreprocessors; and memory for storing instructions to be executed by theone or more processors, the stored instructions to: determine a queuingdelay of the transmission, wherein the queuing delay corresponds to thedifference of an average round trip time of the data packets and a baseround trip time of the data packets; determine a loss rate of thetransmission, wherein the loss rate corresponds to the ratio of a numberof data packets lost in the transmission to the number of data packetstransmitted; compare the queuing delay to a threshold queuing delay;compare the loss rate to a threshold loss rate; in response to adetermination that the queuing delay is greater than the thresholdqueuing delay and the loss rate is less than the threshold loss rate,reset the size of the congestion window in accordance with a firstfunction of a current size of the congestion window and the queuingdelay, wherein at equilibrium the first function generates a valueinversely related to an excess queuing delay, which corresponds to thedifference between the queuing delay and the threshold queuing delay; inresponse to a determination that the queuing delay is less than thethreshold queuing delay and the loss rate is greater than the thresholdloss rate, reset the size of the congestion window in accordance with asecond function of the current size of the congestion window and theloss rate, wherein at equilibrium the second function generates a valueinversely related to an excess loss rate, which corresponds to thedifference between the loss rate and the threshold loss rate; inresponse to a determination that the queuing delay is greater than thethreshold queuing delay and the loss rate is greater than the thresholdloss rate, reset the size of the congestion window in accordance with athird function of the current size of the congestion window, the queuingdelay, and the loss rate, wherein at equilibrium the third functiongenerates a value inversely proportional to a weighted sum of the excessqueuing delay and excess loss rate.
 4. The apparatus of claim 3, whereinthe weighted sum is a convex sum.
 5. A non-transitory computer readablestorage medium, storing one or more programs for execution by one ormore processor of an apparatus that includes a transceiver to transmitpackets over a communication channel to a receiver; wherein the one ormore programs are for execution by the one or more processors of theapparatus so as to perform a method comprising: transmitting a number ofdata packets over a communication channel from the transmitting deviceto a receiver; determining a queuing delay of the transmission, whereinthe queuing delay corresponds to the difference of an average round triptime of the data packets and a base round trip time of the data packets;determining a loss rate of the transmission, wherein the loss ratecorresponds to the ratio of a number of data packets lost in thetransmission to the number of data packets transmitted; comparing thequeuing delay to a threshold queuing delay; comparing the loss rate to athreshold loss rate; in response to a determination that the queuingdelay is greater than the threshold queuing delay and the loss rate isless than the threshold loss rate, resetting the size of the congestionwindow in accordance with a first function of a current size of thecongestion window and the queuing delay, wherein at equilibrium thefirst function generates a value inversely related to an excess queuingdelay, which corresponds to the difference between the queuing delay andthe threshold queuing delay; in response to a determination that thequeuing delay is less than the threshold queuing delay and the loss rateis greater than the threshold loss rate, resetting the size of thecongestion window in accordance with a second function of the currentsize of the congestion window and the loss rate, wherein at equilibriumthe second function generates a value inversely related to an excessloss rate, which corresponds to the difference between the loss rate andthe threshold loss rate; in response to a determination that the queuingdelay is greater than the threshold queuing delay and the loss rate isgreater than the threshold loss rate, resetting the size of thecongestion window in accordance with a third function of the currentsize of the congestion window, the queuing delay, and the loss rate,wherein at equilibrium the third function generates a value inverselyproportional to a weighted sum of the excess queuing delay and excessloss rate.
 6. The non-transitory computer readable storage medium ofclaim 2, wherein the weighted sum is a convex sum.
 7. A method ofcontrolling size of a congestion window, comprising: at a transmittingdevice: transmitting a plurality of data packets over a communicationchannel from the transmitting device to a receiver; determining aqueuing delay of the transmission, wherein the queuing delay correspondsto the difference of an average round trip time of the data packets anda base round trip time of the data packets; determining a loss rate ofthe transmission, wherein the loss rate corresponds to the ratio of anumber of data packets lost in the transmission to the number of datapackets transmitted; comparing the queuing delay to a threshold queuingdelay; comparing the loss rate to a threshold loss rate; determining anexcess queuing delay, wherein excess queuing delay corresponds to thedifference between the queuing delay and the threshold queuing delay;determining an excess loss rate, wherein excess loss rate corresponds tothe difference between the loss rate and the threshold loss rate; inresponse to a determination that the queuing delay is greater than thethreshold queuing delay and the loss rate is greater than the thresholdloss rate, resetting the size of the congestion window in accordancewith a function of the current size of the congestion window, thequeuing delay, and the loss rate, wherein at equilibrium the functiongenerates a value inversely proportional to a weighted sum of the excessqueuing delay and excess loss rate.
 8. The method of claim 7, whereinthe weighted sum is a convex sum.
 9. An apparatus for controlling sizeof a congestion window, the apparatus comprising: a transceiver totransmit a plurality of packets over a communication channel to areceiver; one or more processors; and memory for storing instructions tobe executed by the one or more processors, the stored instructions to:transmit a plurality of data packets over a communication channel fromthe transmitting device to a receiver; determine a queuing delay of thetransmission, wherein the queuing delay corresponds to the difference ofan average round trip time of the data packets and a base round triptime of the data packets; determine a loss rate of the transmission,wherein the loss rate corresponds to the ratio of a number of datapackets lost in the transmission to the number of data packetstransmitted; compare the queuing delay to a threshold queuing delay;compare the loss rate to a threshold loss rate; determine an excessqueuing delay, wherein excess queuing delay corresponds to thedifference between the queuing delay and the threshold queuing delay;determine an excess loss rate, wherein excess loss rate corresponds tothe difference between the loss rate and the threshold loss rate; inresponse to a determination that the queuing delay is greater than thethreshold queuing delay and the loss rate is greater than the thresholdloss rate, reset the size of the congestion window in accordance with afunction of the current size of the congestion window, the queuingdelay, and the loss rate, wherein at equilibrium the function generatesa value inversely proportional to a weighted sum of the excess queuingdelay and excess loss rate.
 10. The apparatus of claim 9, wherein theweighted sum is a convex sum.
 11. A non-transitory computer readablestorage medium, storing one or more programs for execution by one ormore processor of an apparatus that includes a transceiver to transmitpackets over a communication channel to a receiver; wherein the one ormore programs are for execution by the one or more processors of theapparatus so as to perform a method comprising: transmitting a pluralityof data packets over a communication channel from the transmittingdevice to a receiver; determining a queuing delay of the transmission,wherein the queuing delay corresponds to the difference of an averageround trip time of the data packets and a base round trip time of thedata packets; determining a loss rate of the transmission, wherein theloss rate corresponds to the ratio of a number of data packets lost inthe transmission to the number of data packets transmitted; comparingthe queuing delay to a threshold queuing delay; comparing the loss rateto a threshold loss rate; determining an excess queuing delay, whereinexcess queuing delay corresponds to the difference between the queuingdelay and the threshold queuing delay; determining an excess loss rate,wherein excess loss rate corresponds to the difference between the lossrate and the threshold loss rate; in response to a determination thatthe queuing delay is greater than the threshold queuing delay and theloss rate is greater than the threshold loss rate, resetting the size ofthe congestion window in accordance with a function of the current sizeof the congestion window, the queuing delay, and the loss rate, whereinat equilibrium the function generates a value inversely proportional toa weighted sum of the excess queuing delay and excess loss rate.
 12. Thenon-transitory computer readable storage medium of claim 11, wherein theweighted sum is a convex sum.